1. Field of the Invention
The present invention relates to a shift shock suppressing system for an automotive power train including a prime mover, such as an internal combustion engine, and an automatic transmission.
2. Description of Related Art
One example of a shift shock suppressing or reducing technology has been disclosed in Japanese Patent Application Laid-open No. 45628/1990.
The conventional shift shock suppressing system, disclosed in the above-identified publication, has a torque varying means for varying the output torque of a prime mover, an input rotation speed sensor for detecting the input rotation speed and an output rotation speed sensor for detecting the output rotation speed of an automatic transmission, respectively, a transmission-ratio calculating means for deriving a nominal transmission-ratio on the basis of a ratio of input and output rotation speeds of the automatic transmission, and a shifting state discriminating means for discriminating on-going shifting state on the basis of the derived nominal transmission-ratio for effecting varying of the torque of the prime mover by the torque varying means.
In the above-mentioned shift shock suppressing system, a vehicle speed sensor, which is conventionally installed on the vehicle for generating a pulse train having a frequency proportional to the rotation speed of the output shaft of the automatic transmission, is employed as an output rotation speed sensor. Therefore, no cost and space problem will arise concerning the output rotation speed sensor. However, it is required to newly install a turbine sensor that generates a pulse train having a frequency proportional to the rotation speed of a turbine of a torque converter, as an input rotation speed sensor. This not only raises the cost for the turbine sensor but also creates a problem in installation space, making application for an existing automatic transmission difficult. In many cases, the additional installation of the turbine sensor requires design modifications for the input portion in the vicinity of the input shaft, such as a transmission casing, an oil pump and so forth.